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From: Andi Kleen <ak@suse.de>
To: Keith Owens <kaos@sgi.com>
Subject: Re: NMI problems with Dell SMP Xeons
Date: Wed, 7 Jun 2006 10:01:40 +0200
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Cc: Ashok Raj <ashok.raj@intel.com>, linux-kernel@vger.kernel.org,
       "Brendan Trotter" <btrotter@gmail.com>
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>
> Two ways:
>
> (1) Boot with a kernel with CONFIG_ACPI=n, so the OS only finds 2 cpus
>     in the MPT instead of the 4 listed by ACPI.
>
> (2) The kernel has ACPI=y, but is booted with maxcpus=2.
>
> In both cases, send_IPI_allbutself() with IPI 2 or an NMI will result
> in a hard reset.

Sounds both like a "Don't do that when it hurts" . I know some people
have religious issues with ACPI, but it's simple a fact that many
modern boxes don't work correctly in obvious or subtle ways without it. 

-Andi